This chapter is from the book

This chapter is from the book

Before REST came I (and pretty much everyone else) never really knew where to put stuff.

—Jonas Nicklas on the Ruby on Rails mailing list

With version 1.2, Rails introduced support for designing APIs consistent with the REST style. Representational State Transfer (REST) is a complex topic in information theory, and a full exploration of it is well beyond the scope of this chapter.1 We'll touch on some of the keystone concepts, however. And in any case, the REST facilities in Rails can prove useful to you even if you're not a REST expert or devotee.

The main reason is that one of the inherent problems that all web developers face is deciding how to name and organize the resources and actions of their application. The most common actions of all database-backed applications happen to fit well into the REST paradigm.

3.1 REST in a Rather Small Nutshell

REST is described by its creator, Roy T. Fielding, as a network architectural style, specifically the style manifested in the architecture of the World Wide Web. Indeed, Fielding is not only the creator of REST but also one of the authors of the HTTP protocol itself. REST and the web have a very close relationship.

Fielding defines REST as a series of constraints imposed upon the interaction between system components. Basically, you start with the general proposition of machines that can talk to each other, and you start ruling some practices in and others out by imposing constraints that include (among others):

Use of a client-server architecture

Stateless communication

Explicit signaling of response cacheability

Use of HTTP request methods such as GET, POST, PUT, and DELETE

The World Wide Web allows for REST-compliant communication. It also allows for violations of REST principles; the constraints aren't always all there unless you put them there. As for this chapter, the most important thing you have to understand is that REST is designed to help you provide services using the native idioms and constructs of HTTP. You'll find, if you look for it, lots of discussion comparing REST to, for example, SOAP—the thrust of the pro-REST argument being that HTTP already enables you to provide services, so you don't need a semantic layer on top of it. Just use what HTTP already gives you.

One of the allures of REST is that it scales relatively well for big systems, like the web. Another is that it encourages—mandates, even—the use of stable, long-lived identifiers (URIs). Machines talk to each other by sending requests and responses labeled with these identifiers. Messages consist of representations (manifestations in text, XML, graphic format, and so on) of resources (high-level, conceptual descriptions of content) or simply HTTP headers.

Ideally at least, when you ask a machine for an XML representation of a resource—say, Romeo and Juliet—you'll use the same identifier every time and the same request metadata indicating that you want XML, and you'll get the same response. And if it's not the same response, there's a reason—like, the resource you're retrieving is a changeable one ("The current transcript for Student #3994," for example).